This application relates generally to a method and device for saving power. More specifically, this application relates to a method and device for using dc-to-dc conversion circuitry in driving a liquid crystal display in a manner that reduced power consumption.
Bistable liquid crystal displays, and in particular, cholesteric liquid crystal displays (ChLCDs), have great potential for use in battery operated devices. The bi-stable property of ChLCDs permits an image to be placed on the display and maintained indefinitely without refresh. Thus, power is consumed only to change the image content, not to maintain it. This can result in significant power savings versus STN or TN displays, especially for relatively static image content.
However, recent application opportunities for ChLCD require even more aggressive power management than afforded by the bi-stability alone. For example, small devices powered by coin cell batteries, such as watches, for example, must achieve the maximum possible number of display updates from a single battery. Typically, it is a design goal to minimize the size (and thus typically reducing the capacity) of the battery as well. A key design challenge for such small displays is generating the ChLCD drive voltages (˜35V) with the efficiency required to produce the desired battery lifetime. This is made difficult by the very small current draw of the display relative to the relatively larger quiescent currents of the dc/dc conversion circuitry.
Accordingly, it would be useful to save power in the operation of the dc-to-dc conversion circuitry. Furthermore, it would be even more useful if such a method would utilize off-the-shelf dc-to-dc converters or circuits that incorporate them.